Electronic balances having setup or calibration modes during which one or more operating parameters are programmed into the balance are well known. In the past, a separate input switch was typically provided for each operating parameter which the user was to program. In complex balances, in which a large number of operating parameters were to be entered, the result was a balance having a multiplicity of switches which was difficult to operate.
An electronic balance having interchangeable weighting platforms in which each weighing platform contains a data storage unit, such as a PROM, for storing operating parameters is shown in U.S. Pat. No. 4,313,509. After connecting a weighing platform to an evaluating device, the stored operating parameters are automatically transmitted to the evaluating device from the weighing platform's data storage unit. Such an arrangement, however, requires that every weighing platform include complex and expensive data storage circuitry.
An electronic balance in which the user can sequentially select operating parameters by means of one of the normal scale controls, such as a TARE switch, is shown in U.S. Pat. No. 4,328,874. However, since selection of a value for each operating parameter is performed sequentially every time the scale is turned on, valuable time is required to set the scale up even when the same operating parameters are to be used from operation to operation.
U.S. Pat. No. 4,412,591 shows an electronic scale in which a single key causes each of a plurality of modes and/or parameters to be selected in sequence. A storage device retains selected parameter values for future use. Access to certain modes or parameters can be prevented by means of jumpers connected to inputs of a microcomputer. In such an arrangement, the use of a single key to sequentially cycle through all the available modes and parameters when it is only desired to input values for a parameter at the end of the sequence requires increased setup time. In addition, inadvertent access to restricted modes and parameters may be granted as a result of an error in the microcomputer's processing of the jumper connection information.
U.S. Pat. No. 4,525,794 shows an electronic balance in which normal scale controls, such as an OFF switch and an ON/TARE switch, are used to select one of several operating modes or parameters. Simultaneous depression of the OFF and ON/TARE switches either permits a user to choose the units in which weight is displayed or, if the balance has the ability to perform parts counting, activates the parts counter mode. Once in the parts counter mode, the balance must be turned off and then on again to return to the ordinary weighting mode. Depression of the ON/TARE switch for a predetermined period of time permits a user to access a calibration routine. A calibration-enable switch connected to an input of a microprocessor can be used to prevent access to the calibration routine. Dead-load adjustment is accomplished by adjusting a potentiometer so that the output signal of a strain guage tranducer is nearly equal to zero when the pan is empty.
In such an arrangement, the need to simultaneously depress a plurality of switches to select a desired operating mode or parameter makes setup difficult. In addition, the inability to perform a weighing operation when in the parts counting mode is inconvenient. Undesired access to the calibration routine may also be granted as a result of an error in the microprocessor's handling of the calibration enable switch information. In addition, since the balance does not indicate if the dead-load adjustment procedure has been properly carried out, there is a possibility that the adjusting potentiometer may be incorrectly set.